teetotal: to not drink alcohol at all
teetotaller: someone who doesn't drink alcohol.

someone who does not drink at all usually for health, religious or personal reasons. not just because they are short on cash or their wife pokes them good in the eye with a broom for coming home drunk.

Someone who has once drunk alcohol to excess habitually, sooner or later, unless that person wants to be dependent on alcohol all thier life, will need to give it up completely. When they do, they usually need to abstain from alcohol for THE REST OF THIER LIFE. This person is called teetotal.

Doug is teetotal. He once drunk lots of booze just to forget who he was. Drinking lots of booze can be fantastically brilliant, but the downside is that you never get anything done.